The present invention relates to a hydraulically operated continuously variable transmissions including a hydraulic pump and a hydraulic motor which are interconnected by a closed hydraulic circuit.
There have been proposed various hydraulically operated continuously variable transmissions for use in automobiles, including a swash-plate axial-plunger hydraulic pump having a pump cylinder coupled to an input shaft and a plurality of pump plungers slidably disposed in respective cylinder holes defined in the pump cylinder in an annular pattern around an axis of rotation of the pump cylinder, the hydraulic pump having an outlet port, a swash-plate axial-plunger hydraulic motor having a motor cylinder coupled to an output shaft and a plurality of motor plungers slidably disposed in respective cylinder holes defined in the motor cylinder in an annular pattern around an axis of rotation of the motor cylinder, the hydraulic motor having an inlet port, and a closed hydraulic circuit interconnecting the hydraulic pump and the hydraulic motor. Power is transmitted by the transmission through relative rotation between the motor cylinder and the pump cylinder.
As disclosed in Japanese Patent Publications Nos. 32-7159 and 41-3208, for example, communication ports arranged at substantially equal angular intervals in communication with the respective cylinder holes in the motor cylinder are defined in the motor cylinder and open at an axial end face thereof in an annular pattern around the axis of rotation of the motor cylinder. An annular distribution ring is disposed eccentrically with respect to the axis of rotation of the motor cylinder and held in slidable contact with the end face of the motor cylinder. Oil discharged from the hydraulic pump is introduced into the distribution ring, whereas oil discharged from the motor cylinder is introduced around the distribution ring.
The outlet and inlet ports of the pump are brought into successive communication with the communication ports in the motor cylinder in response to relative rotation between the distribution ring and the motor cylinder for reciprocally moving the annularly arranged motor plungers.
Another known distribution ring has a suction port for introducing oil discharged from the pump into those cylinder holes which are in the expansion stroke and a discharge port for discharging oil from those cylinder holes which are in the contraction stroke, the suction and discharge ports being of an annular shape along the annular pattern of the communication ports. In this arrangement, the annularly arranged communication ports are successively brought into communication with the suction and discharge ports of the distribution ring in response to rotation of the motor cylinder for reciprocally moving the annularly arranged motor plungers while drawing in and discharging working oil.
The distribution ring in the above conventional arrangements is fitted in a fluid-tight manner over a fixed shaft mounted in a casing through a seal member such as an O-ring. When the motor cylinder rotates at high speed, the distribution ring tends to rotate therewith, bringing the ports out of registry or damaging the O-ring.